with lots of stems 3oz with 4 sticks of butter might be on the mild side.

12 hours is probably better. 4 hours works basically the same. If I start in the morning I let it cook 4 or 5 hours, if I start at night I let it sit for 2 or 3 hours with me watching it so I am sure it wont get too hot and then I go to bed and finish up in the morning.

Since you found that last paragraph funny I will tell you more tales of my butter making adventures. This one time I was making a big batch and woke up after passing out and realized that all the food in the house had weed in it and I was starving. Brownies, brownies, everywhere and not a bite to eat. My blood sugar was so low, it was bad. I managed to drag myself in my butter stained cloths to the McDonalds to order a burger. I think the people there thought I was crazy as I was holding by self up against the counter and stumbling around. Bad cotton mouth made it hard to order.